Description

The
readdir()
function returns a pointer to a dirent structure
representing the next directory entry in the directory stream pointed
to by dirp.
It returns NULL on reaching the end of the directory stream or if
an error occurred.

The only fields in the
dirent
structure that are mandated by POSIX.1 are:
d_name[],
of unspecified size, with at most
NAME_MAX
characters preceding the terminating null byte (aq\0aq);
and (as an XSI extension)
d_ino.
The other fields are unstandardized, and not present on all systems;
see NOTES below for some further details.

The data returned by
readdir()
may be overwritten by subsequent calls to
readdir()
for the same directory stream.

The
readdir_r()
function is a reentrant version of
readdir().
It reads the next directory entry from the directory stream
dirp,
and returns it in the caller-allocated buffer pointed to by
entry.
(See NOTES for information on allocating this buffer.)
A pointer to the returned item is placed in
*result;
if the end of the directory stream was encountered,
then NULL is instead returned in
*result.

Return Value

On success,
readdir()
returns a pointer to a
dirent
structure.
(This structure may be statically allocated; do not attempt to
free(3)
it.)
If the end of the directory stream is reached, NULL is returned and
errno
is not changed.
If an error occurs, NULL is returned and
errno
is set appropriately.

The
readdir_r()
function returns 0 on success.
On error, it returns a positive error number (listed under ERRORS).
If the end of the directory stream is reached,
readdir_r()
returns 0, and returns NULL in
*result.

Errors

EBADF

Invalid directory stream descriptor dirp.

Attributes

Conforming To

SVr4, 4.3BSD, POSIX.1-2001.

Notes

Only the fields
d_name
and
d_ino
are specified in POSIX.1-2001.
The remaining fields are available on many, but not all systems.
Under glibc,
programs can check for the availability of the fields not defined
in POSIX.1 by testing whether the macros
_DIRENT_HAVE_D_NAMLEN,
_DIRENT_HAVE_D_RECLEN,
_DIRENT_HAVE_D_OFF,
or
_DIRENT_HAVE_D_TYPE
are defined.

The value returned in
d_off
is the same as would be returned by calling
telldir(3)
at the current position in the directory stream.
Be aware that despite its type and name, the
d_off
field is seldom any kind of directory offset on modern filesystems.
Applications should treat this field as an opaque value,
making no assumptions about its contents; see also
telldir(3).

Other than Linux, the
d_type
field is available mainly only on BSD systems.
This field makes it possible to avoid the expense of calling
lstat(2)
if further actions depend on the type of the file.
If the
_BSD_SOURCE
feature test macro is defined,
then glibc defines the following macro constants
for the value returned in
d_type:

DT_BLK

This is a block device.

DT_CHR

This is a character device.

DT_DIR

This is a directory.

DT_FIFO

This is a named pipe (FIFO).

DT_LNK

This is a symbolic link.

DT_REG

This is a regular file.

DT_SOCK

This is a UNIX domain socket.

DT_UNKNOWN

The file type is unknown.

If the file type could not be determined, the value
DT_UNKNOWN
is returned in
d_type.

Currently,
only some filesystems (among them: Btrfs, ext2, ext3, and ext4)
have full support for returning the file type in
d_type.
All applications must properly handle a return of
DT_UNKNOWN.

Since POSIX.1 does not specify the size of the
d_name
field, and other nonstandard fields may precede that field within the
dirent
structure, portable applications that use
readdir_r()
should allocate the buffer whose address is passed in
entry
as follows:

See Also

Colophon

This page is part of release 3.80 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
http://www.kernel.org/doc/man-pages/.

License & Copyright

Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
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References consulted:
Linux libc source code
Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
386BSD man pages
Modified Sat Jul 24 16:09:49 1993 by Rik Faith (faith@cs.unc.edu)
Modified 11 June 1995 by Andries Brouwer (aeb@cwi.nl)
Modified 22 July 1996 by Andries Brouwer (aeb@cwi.nl)
2007-07-30 Ulrich Drepper , mtk:
Rework discussion of nonstandard structure fields.
2008-09-11, mtk, Document readdir_r().